This invention generally relates to the inspection of glass containers for a condition known in the art as "leaner". More specifically, this invention relates to a laboratory instrument for measuring "leaner" conditions which is insensitive to operator variations. Most particularly, this invention relates to such an instrument which uses an air back pressure signal generated in response to movement of a follower member in contact with the container as the source of "leaner" information.
One of the defects which may occur in glass containers is that known as "leaner". A "leaner" is a glass container whose top portion is displaced or offset from the vertical center line of the entire container an excessive amount. This is an undesirable condition because it can create problems in filling and capping operations. The fill tubes for glass containers are designed to enter the container along the vertical center line of the container. If the top portion, including the finish, is offset an excessive amount from the center line, a possible jam condition exists. In the past, laboratory checks of selected samples from the manufacturing line for lean used a dial indicator system. This required operator readings of the dials and some skill to hold the container in the precise orientation required for repeatable readings. In addition, the operator had to manually divide the readings from the dial indicator by two. The result has been some variation in readings and a problem in comparing readings over a period of time. We have eliminated this problem by removing the necessity of operator interaction during the measurement process. Our instrument requires only that the operator chuck the container to be measured. Then, the movement of the top portion is measured as a function of a fluid back pressure which is then further processed to give a numerical read out equal to the actual lean or deviation from the vertical center line. One example of a prior art device may be seen in U.S. Pat. No. 3,289,834. Other devices to measure container lean are on line instruments and measure lean as the container is moving. Examples of such instruments may be seen in U.S. Pat. Nos. 3,548,890 and 3,754,123.